The present disclosure relates to magnetic materials, and in particular to soft magnetic materials useful as core materials of inductive components.
The inductive components used in electronics and electronic devices require use of magnetic materials. Ideal magnetic materials for inductive components possess high saturation magnetization, high initial permeability, high resistivity, low magnetic power loss, low eddy current loss, low dielectric power loss, high Curie temperature, stable magnetic and electrical properties over a range of temperatures, good mechanical strength.
To date, high frequency magnetic components use ferrites as core materials, which have been in use for more than five decades. However, ferrites possess several major disadvantages, including low permeability when compared to metallic materials, poor performance at frequencies of greater than 100 MHz, low Curie temperature, and complex manufacturing procedures. Currently, there is no method available for producing soft magnetic materials with properties superior to ferrites in the high frequency range (greater than 100 MHz), that are also capable of being manufactured in bulk quantity.
Current methods for processing conventional micrometer-sized soft magnetic materials are designed to reduce the total core loss by reducing eddy current loss. Three types of soft magnetic materials are presently used: metallic ribbons, powdered metals, and powdered ferrites. Metallic ribbon materials comprise Fexe2x80x94Ni, Fexe2x80x94Co, and Fexe2x80x94Si alloys, manufactured in the form of stripes or ribbons using a metallic metallurgy approach. These metallic alloys are used in the frequency range of 10 to 100 kHz.
Powdered metal materials are composites consisting of a metallic magnetic phase (Fe, Co or their alloys) and a nonmagnetic insulating phase. This type of material is made by powder metallic metallurgy techniques. Powder materials are used in the frequency range of 50 kHz to 500 kHz.
Ferrites include materials such as spinel ferrites (e.g., (Ni, Zn)Fe2O4 or (Ni,Zn)Fe2O4), hexagonal ferrites (e.g., Me2Z, wherein Z=Ba3Me2Fe24O, and Me denotes a transition metal element), and garnet ferrites (e.g., Y3Fe5O12). Ferrites are made by ceramic processing, and are used in the frequency range from 100 kHz to 100 GHz.
There are a number of disadvantages associated with use of the currently available soft magnetic materials. In conventional micrometer-sized magnetic materials, each particle possesses many magnetic domains (or multidomains), which cause interference or resonance. Domain wall resonance restricts the frequency characteristics of the initial permeability. When the size of the magnetic particle is smaller than the critical size for multidomain formation, the particle is in a single domain state. Domain wall resonance is avoided, and the material can work at higher frequencies.
None of the three types of magnetic materials meet all of the above-mentioned requirements in soft magnetic applications due to their associated large core loss. Metallic magnetic alloy ribbons have excellent fundamental magnetic properties such as high saturation magnetization, low intrinsic, high initial permeability, and high Curie temperature. However, their extremely low resistivity (10xe2x88x926 Ohm-cm) makes them difficult to be use beyond 1 MHz. In addition, the mechanical strength of the ribbons is very poor. Powder materials have higher resistivity and, consequently, can be used at higher frequency range, but their permeability is low. Ferrites are the only practical choice when the working frequency for a device is beyond 1 MHz, but the magnetic properties of ferrites in high frequency range are actually poor. Although extensive efforts have been directed to improving the performance of these materials, very limited progress was obtained.
To date, there appears to be no prior art relating to the use of a nanostructured materials in bulk soft magnetic applications. As used herein, nanostructured materials have ultrafine grains or particles of less than 100 nanometers (nm). A feature of nanostructured materials is the high fraction of atoms (up to 50%) that reside at grain or particle boundaries. Such materials have substantially different, very often superior, chemical and physical properties compared to conventional micrometer-sized grain counterparts having the same composition.
A variety of methods have been developed to produce nanostructured particulate materials, for example production by condensation from the vapor phase. This inert gas condensation methodology has been scaled-up by Nanophase Technologies to produce n-TiO2 and Al2O3 in commercial quantities. Another technique for making nanostructured metal and ceramic powders is by mechanical milling at ambient or at liquid nitrogen (cryomilling) temperature. A third approach is chemical synthesis from inorganic or organic precursors, which has been used to produce nanostructured WC/C.
Recently, nanostructured FeMO (wherein M is Hf, Zr, Si, Al or rare-earth metal element) thin films have been obtained by Hadjipanayis et al, and Hayakawa et al, via atomic deposition. These are nanostructured composite thin films deposited on substrates, and the thin film is composed of nanostructured magnetic particles surrounded by an amorphous insulating phase. However, the atomic deposition approach is limited to thin film application, and is not suitable for bulk materials.
Fe/silica nanostructured composites have been proposed for use in magnetic refrigeration application. The nanostructured composites are a mixture of iron particles with silica ceramic, but such composites are limited to magnetic refrigeration, and cannot be used for high frequency magnetic applications. The synthesis of magnetic nanostructured composites using a wet chemical synthesis technique has been described, wherein a Fen/BN nanostructured composite was prepared by the ammonolysis of an aqueous mixture solution of FeCl3, urea, and boric acid, followed by the thermochemical conversion. While the synthesis of other magnetic nanostructured composite systems have been described, none of these materials is suitable for high frequency soft magnetic applications for reduced core loss. There accordingly remains a need in the art for compositions and methods for bulk manufacture of soft magnetic materials, especially bulk materials useful above about 1 MHz.
The above-described drawbacks and disadvantages are overcome or alleviated by a magnet/insulator nanostructured composite material comprising nanostructured magnetic particles embedded in an insulating matrix.
A method to manufacture such materials comprises fabricating a precomposite from a precursor composition; forming magnetic nanostructured particles surrounded by a dielectric layer from a precomposite; and passivating the surface of the surrounded nanostructured particles.
A method for forming a consolidated bulk magnetic/insulator nanostructured composite comprises preparing a ready-to-press nanostructured composite powders comprising a nanostructured metal core and a dielectric layer; consolidating the ready-to-press powder into a green compact; shaping the green compact; and annealing the shaped compact.